Enhancing the photocatalytic properties of doped TiO2 nanowires grown by seed-assisted thermal oxidation

In the present paper, an investigation of the structural, optical, and photo-catalytical properties of TiO2 nanowires (NWs) was conducted. The NWs were synthesized on a Si substrate by thermal oxidation of a thick (4 mu m) Ti film covered by a thin (similar to 5 nm) Au film. The annealing process at 750 degrees C produced a 1.7 mu m thick NWs TiO2 layer over a 3 mu m thick TiO2 film. Characterization techniques show that TiO2 NWs are in rutile phase and have gold nanoparticles on top. Fe-doped TiO2 NWs were synthesized to increase photoactivity in the visible range. The doping was performed using an unusual strategy, that is, implanting Fe+ ions into the Ti layers before the growth of the TiO2 NWs. The defectiveness introduced by the ion implantation is avoided and precise control of the doping is achieved. The photocatalytic properties were studied by following the degradation of methylene blue. In order to increase the photo-degradation rate under UV light of undoped NWs, two different strategies have been followed: 1) deposition of Pt nanoparticles on the front or on the rear side of the samples, and 2) thermal annealing in a reductive environment. A three-fold activity enhancement is obtained and discussed. Photocatalytic activity in the visible range was also measured for the Fe-doped samples, showing good activity, which was further improved by using the same strategies implemented under UV irradiation.